Protective system



July 30, 1940. P. E. KNUDSEN 2,209,527

' PROTECTIVE SYSTEM Filed June 4,'1953 D *M il 4272?..1. S

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Patented July 30, 1940 UNITED STATES PATENT FFiiJE PROTECTIVE SYSTEM Application June 4, 1938, Serial No. 211,959

6 Claims.

The present invention relates to annunciator or alarm systems, and it has particular relation to an alarm system for use in connection with panels of tempered glass.

One object of the invention is to provide an alarm system of the foregoing type which is simple, does not mar or obscure the glass, does not draw electrical energy during normal service, and does not require the use of nne, embedded wires that are subject to breakage or to burning out.

This and other objects of the invention will be apparent from consideration of the following specifications and the appendant claims.

It has heretofore been proposed to protect Windows, showcases, glass doors and the like structures from unauthorized entrance by forming them of glass in which were embedded wires constituting electrical conductors to a protective device and as an alarm. Breakage of such glass caused electrical actuation of the protective device. The wires in the glass were, of course, unsightly and moreover they served towarn intruders of the presence of the protective device. They also continuously consumed electrical energy, and wer-e subject to breakage and to burning out.

Tempered glass when scratched or cracked will immediately crack into many small fragments, but if the glass is in a frame, the fragments will remain in place. However, cracking is attended by substantial lateral expansion. This expansion may amount to l per cent or 2 per cent so that a sheet of glass of the size of an ordinary window may expand as much as 2 inches. It is now proposed to utilize this expansion to actuate an alarm or other protective device.

A suitable embodiment of apparatus for use in practicing the invention is disclosed in the drawing in which Figure 1 is an elevational View of a window disposed in a wall and embodying the features of the present invention.

Figure 2 is a fragmentary cross-sectional View taken substantially upon the line I11I of Figure 1.

Figure 3 is a fragmentary cross-sectional view taken through the electrical contact making device after the latter has been actuated by the breakage of the glass. In the drawing, like numerals refer to like parts throughout.

The construction disclosed in the drawing comprises a building wall 5 in which is formed an opening 6 spanned by lintel l. Jambs B may also be disposed in the opening to provide a suitable nish about the opening. A window il disposed in the opening preferably comprises sheet of glass which has been tempered by heating to a temperature of 1100 or i209 degrees and suddenly chilling by means of a blast of air or by 'f5 dipping into a bath of oil. As a result of chilling the strength of the glass is substantially increased and may even approximately equal that of cast iron. However, the glass is under internal strain which, if the glass is ruptured by J0 scratching or breakage, will result in immediate automatic shattering of the entire sheet into small diced fragments which are practically harmless to the object or person struck thereby, and the glass expands laterally to an extent of '35 1 per cent or 2 per cent. In order to utilize this expansion to actuate a protective device, the margins of the glass are enclosed by a channellike frame l2, having backwardly bent edges I3, that resiliently and slidably Contact with the lnner side walls of an ornamental frame it, preferably formed of aluminum or some other corrosion resistant material. The specinc construction of this ornamental frame does not constitute a portion of the present invention and ac- 25 cordingly it is not described in detail.

The channels l2 may carry about their outer peripheries one or more plugs comprising projecting prongs I6, which at their extremities are provided with knobs l1, adapted to bridge the 30 space between a pair of spring contact points i8, constituting a jack. These contact points are secured to the inner walls of the frame M, and are connected to suitable conductors itl, which lead to a protective device 2i, such as a buzzer 35 or the like disposed in any convenient position. It will be apparent that various types of switch constructions may be employed in the system. For example, the positions of the plug and the jack may be transposed, The jack switch may be re- 40 placed by a snap switch, the actuating element of which contacts with the edge of the glass. The expansion of the glass may also be utilized to tilt a conventional mercury switch.

A suitable source of electrical energy, e. g. a 45 battery or galvanic cell 23, is connected into the circuit of the switch and the protective device.

The mode of operation of the apparatus is practically self evident from the foregoing description. The channel l2, carrying the plug 50 with knob I1, is simply disposed upon the edge of the glass panel and the jack comprising the prongs or clips i8, is secured in position within the frame I4, by welding or by means of rivets or screws or by any other convenient instrumentalities. The hollow frame, I4, is then secured about the edge of the glass in such manner that the reexly bent edges I3, of the channel are brought into contact with the inner side walls of the frame. Afterwards the frame is secured to the lintel I of a building by means of suitable bolts, e. g., the bolts 211 and the leads I9 are connected up with the protective device. So long as the glass II remains intact, the contact knob I'I is retained in retracted position shown in Fig. 1 with respect to the prongs I8, and no current flows through the circuit. However, if the glass II is broken by any instrumentality, for example, by scratching the surface thereof with a diamond or with a glass cutter, the panel instantly shatters into innumerable small, diced fragments. At the same time there is a lateral expansion of the glass and the knob I'I is push-ed upwardly between the prongs as indicated in Figure 3 to establish an electrical circuit which actuates the protective device 2I. It will be apparent that the gripping action, exerted by the contact springs I8, and the springs I3, respectively, upon the knob I'I, and the side walls of the hollow frame I4, is sufficient to retain the plug in position and to maintain the closed circuit in the apparatus even though the glass plate is subsequently completely broken out to permit entrance of the intruder into the interlor of the structure which is to be protected. Accordingly, the action of the protective device is continued until it is shut off by an authorized operator.

The advantages of the present structure over those heretofore employed are manifold. For example, there are no Wires within the glass which may become broken and, therefore, destroy the utility of the apparatus. Furthermore, during normal service, there is no ovv of current through the wires and the expense incident to supplying such current is obviated. Likewise the possibility of the wires becoming overheated by reason of the prolonged flow of current is prevented. It will be apparent that in a structure in Which the wires carrying the signaling current are carried within the glass there is possibility of the glass being unequally heated by the electrical current and therefore, there is a chance for breakage due to excessive internal stress within the glass itself. All these possibilities, of course, are obviated by use of the present invention. Moreover, it is to be understood that a tempered glass, such as is employed in practicing the present invention, is much stronger than an ordinary glass and in fact possesses a mechanical strength approximately equal to that of cast iron. Therefore, it is much less likely to be subject to accidental or intentional breakage than a conventional glass.

Protective systems embodying the present invention may be employed in connection with various structures. For example, they are applicable to windows of stores, prisons or practically any other building where it isdesired to prevent entrance through the windows. Likewise, they are applicable to panels of show cases and cabinets. A further place of application would be to the glass in automobilesin which breakage might be utilized to set olf an alarm to frighten tion or from the scope of the appended claims.

What I claim is:

1. A building comprising a wall having an opening formed there-in, a closure in the opening, the closure comprising a plate of tempered glass adapted upon rupture to shatter into fragments with simultaneous substantial expansion of the plate in the plane thereof, an electrically actuated protective device appropriately disposed with respect to the building, a switch comprising a fixed element and a movable element, one of said elements carrying contact means in the circuit of the protective device, and the other element having circuit closing contact means for engaging the first-mentioned means to close the switch, and being disposed for actuation by the edge of the plate upon rupture and lateral expansion of the latter, to bring the two contact means into engagement.

2. A construction as defined in claim l in which the channel and the switch are disposed in a hollow sash frame which is adapted to be secured in an opening in the chamber.

3. In a building comprising a wall having an opening with a marginal frame disposed therein, a closure for the opening disposed in the frame, the closure comprising a plate of tempered glass,

a protective device and means associated with an edge of the glass which upon breakage and lateral expansion of the glass effects actuation of the protective device.

4. In a building comprising a wall having an opening with a marginal frame disposed therein,

a closure in the frame, the closure comprising a plate of tempered glass, an electrically operated protective device, a circuit therefor, means associated with an edge of the glass which upon breakage and lateral expansion of the glass closes the circuit to operate the protective device.

5. A combined protective and closure system il for an opening in a Wall, said system comprising a plate of tempered glass, which plate upon'rup ture is adapted simultaneously to shatter and laterally to expand, the edges of the plate being encased by a channel, an electrically controlled protective device, an electrical switch in series with the device and being associated with the channel and comprising a relatively movable and relatively fixed contact element, the former being so disposed with respect to the channel that it is actuated by the channel to bring the contact elements into engagement to close the circuit of the protective device upon Vbreakage and lateral expansion of the glass.

6. A combined closure and protective system for an opening forme-d in a building wall, said system comprising a plate of tempered glass constituting the closure for said opening, the edges of the glass being encased by a channel, an'electrically actuated protective device, an electrical switch associated with the edge of the plate and being in series with said device and comprising a relatively movable and a relatively fixed contact element, the movable element being disposed to be actuated into engagement with the xed element by the channel upon rupture and resultant lateral expansion of the glass carrying the channel, said channel being of spring material and having outwardly and reflexly bent edge portions, a hollow frame enclosing the channel and carrying the fixed element of the switch, said frame having guidesurfaces contacting with the edge portions of the channel. p

PERCY E. KN'UDSEN." 

